I would wrap the Chart in a Tablix object. I would add a Tablix and associate it with the same dataset as the chart. I would delete all the columns bar one, and delete the Header and Footer rows. I would make the Details Row not Visible.
I would add a Row Group on a calculation to group by row number in groups of 20 e.g.
= RowNumber ( Nothing ) Mod 20
For the Group Header Row, I would resize it to fit the chart, then cut the Chart and paste it inside the Group Header row.